ath6kl: Fix WLAN tethering authentication problem.

ath6kl: Fix WLAN tethering authentication problem.

When enabling WLAN tethering, a new AP is visible and a STA could
connect to it. When the STA tries to authenticate to the newly created
AP, the WPA authentication mechanism is stuck in the 1/4 msg of 4-Way
Handshake.

In ath6kl_rx(), the ath6kl_find_sta() function is looking for the
h_source field of the Ethernet frame header received by the STA. The
datap pointer that points to the Ethernet frame header is incorrect,
and was pointing at the wrong offset in the buffer.

This commit adds a pad_before_data_start offset to set the datap pointer
to the Ethernet frame header. datap->h_source parameter is now really
pointing to the source ethernet address and the authentication process
can continue.

Signed-off-by: Pierre Le Magourou <plemagourou@aldebaran.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>